JP2018515688A - Method and apparatus for reaction control - Google Patents

Abstract

A continuous annealing furnace (1) for annealing a steel strip (5), the continuous annealing furnace (1) comprising a reaction chamber (2) in which the steel strip (5) is transported vertically, The reaction chamber (2) includes an opening (4) (also referred to as a reactant opening) fed with a reactant, located at the top or bottom of the reaction chamber (2), wherein the reaction chamber (2) is It further includes another opening (3) (also referred to as an inert gas opening) to which an inert gas is supplied, and the inert gas opening (3) is located on the side of the reaction chamber (2). [Selection] Figure 2

Description

  The present invention relates to an apparatus and method for controlling surface reactions on steel sheets transported in a continuous galvanizing or annealing line.

  High-strength steel grades generally have high content elements such as silicon, manganese, and chromium (typically 0.5-2 wt%, 1.5-6 wt%, and 0.3-1 wt%, respectively) %)including. It is difficult to coat high strength steel grades. This is because oxide layers of these elements are formed during annealing prior to immersion in the galvanizing bath. This oxide layer impairs the wettability of the steel surface when submerged in the bath. As a result, uncovered areas of the coating and poor adhesion are obtained.

A well-known method for improving the wetting of these steel grades is to fully oxidize the steel surface in a special chamber when the steel typically has a temperature of 600-750 ° C. The resulting oxide layer contains a large amount of iron oxide, which is then reduced at the end of the heating and holding zone of the annealing furnace and subsequent heat treatment. The aim is to obtain an oxide thickness of about 50-300 nm, which corresponds to iron oxides of ² g / m ² or less.

  There are various ways to oxidize the steel surface before the reduction step. For example, the oxidation can be performed in a direct combustion furnace that performs combustion with excess air. Another method is to perform this oxidation in a dedicated chamber located in the center of the annealing furnace and fed with a mixture of nitrogen and oxidant. Such an implementation is described in patent EP2010690B1 and FIG. This oxidation zone is separated from the rest of the annealing furnace by a seal to minimize the introduction of oxidant in the first and final zones.

  The formation of the oxide layer must be carefully controlled to avoid the formation of layers that are too thick or too thin. In the first case, the reduction in the final part of the furnace can be incomplete due to lack of time. In that case, it is known that the oxide can stick to the furnace roller and cause defects. In the second case, the oxide layer is not sufficiently effective. This is because the oxidation of the alloying elements cannot be sufficiently prevented, and thus the wetting of the liquid metal bath is not sufficiently improved.

  The formation of the oxide layer is guided by three main parameters: strip temperature, oxygen concentration in the chamber atmosphere, and transport of that oxygen to the steel surface. Since the edge of the sheet does not have the same boundary conditions and turbulence as the center of the sheet, the transport of oxidant to the edge is different from the center of the sheet. Similar to high edge cooling in the process line, edge oxidation tends to be even stronger. The width affected by this over-oxidation ranges from 1-10 cm depending on the design of the oxidation chamber and the processing parameters used.

  Therefore, to obtain a uniform oxide thickness, it is necessary to have a controllable system that can accommodate frequent strip width changes (typically 900-2000 cm) in a continuous galvanizing line. .

  Although mechanical systems can be designed with variable injection zones, this method is not industrially reliable due to the high temperature strips and induced thermal expansion of the material. This becomes a real problem. In other words, since all steel sheets do not require such an oxidation step, the oxidation chamber is only occasionally used.

  The present invention is a continuous annealing furnace for annealing a steel strip, the continuous annealing furnace comprising a reaction chamber in which the steel strip is transported vertically, the reaction chamber being at the top or bottom of the reaction chamber. And includes an opening for supplying a reactant (also referred to as a reactant opening), and the reaction chamber further includes another opening (also referred to as an inert gas opening) for supplying an inert gas. , Relates to a continuous annealing furnace in which the inert gas opening is located to the side of the reaction chamber.

According to a particularly preferred embodiment, the furnace according to the invention further discloses at least one or a suitable combination of the following features:
-The inert gas opening is positioned in such a way that it is downstream of the reactant stream from the reactant opening;
The furnace includes one or more inert gas openings on each side of the reaction chamber;
The furnace includes means for controlling the flow rate and temperature of the inert gas;
The furnace includes means for separately controlling the flow of inert gas on each side of the reaction chamber;
The reaction chamber comprises an extraction opening for avoiding overpressure inside the reaction chamber, said extraction opening being downstream of the reactant flow and the inert gas flow leaving the reactant opening and the inert gas opening, respectively; Positioned as;
The distance between the sides of the reaction chamber and the edge of the steel strip is 75-220 mm, preferably 100-200 mm, more preferably 100 mm;
The reaction chamber includes a reactant opening facing each side of the steel strip;
The reaction chamber is an oxidation chamber and the reactant is an oxidant.

  The present invention also includes a step of vertically injecting the reaction chamber of the continuous annealing furnace, including the step of injecting an inert gas from the side in the reaction chamber, and the step of injecting a reactant upstream of the inert gas flow in the reaction chamber. It relates to a method for controlling the surface reaction on a steel strip that runs in a direction.

According to a particularly preferred embodiment, the method according to the invention further discloses at least one or a suitable combination of the following features:
The reaction chamber is an oxidation chamber, the reactant is an oxidant, and the oxygen content of the oxidant is 0.01 to 8% by volume, preferably 0.1 to 4% by volume;
The inert gas flow rate is 5 to 70 Nm ³ / h, preferably 10 to 60 Nm ³ / h;
When the reaction of the steel strip is carried out by injecting the reactants at the top of the reaction chamber, the inert gas temperature is 200-50 ° C. below the steel strip temperature, and the reaction of the steel strip is at the bottom of the reaction chamber The inert gas temperature is 200-50 ° C. higher than the steel strip temperature;
There is a step of extracting a gas containing inert gas and reactants, the flow rate of the extracted gas being calculated based on the pressure difference between the inside of the reaction chamber and the other part of the continuous annealing furnace.

  Finally, the invention also provides that the steel strip has an oxide layer at the exit of the oxidation chamber, the oxide layer per surface area between the value at the center of the steel strip and the maximum value at the edge of the steel strip. It relates to a steel strip obtained by the above method, wherein the increase in mass is less than 15%, preferably less than 10%.

  The invention will be described in more detail below on the basis of exemplary drawings. The present invention is not limited to the exemplary embodiments. All features described and / or shown herein can be used alone or in different combinations in the embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings, in which:

FIG. 1 schematically represents an annealing furnace comprising an oxidation zone according to the prior art.

FIG. 2 schematically represents an oxidation chamber according to the invention with a side opening for injecting an inert gas.

FIG. 3 represents the upper part of the oxidation chamber according to the invention with a lateral opening for injecting oxidant.

FIG. 4 represents a lateral opening of an oxidation chamber with a stiffener according to an embodiment of the invention.

FIG. 5 represents the lower part of an oxidation chamber with an extraction opening according to an embodiment of the invention.

FIG. 6 represents the lower part of an oxidation chamber with an extraction opening according to another embodiment of the invention.

FIG. 7 represents the mass evolution per unit area of the oxide layer through the width of the strip when there is no lateral injection of inert gas.

FIG. 8 represents the mass evolution per unit area of the oxide layer through the width of the strip when there is a lateral injection of inert gas.

FIG. 9 represents control means for separately adjusting the inert gas flow rate on each side of the oxidation chamber and control means for controlling oxidant injection at the top of the oxidation chamber in accordance with the present invention.

  The present invention seeks to provide an apparatus and method for controlling the surface reaction of a sheet edge without a mechanical system. The surface reaction can be any reaction that can occur in a section of an annealing furnace, such as a reduction reaction or a nitridation reaction, which is fed with the appropriate reactants. Indeed, the problem of forming layers with different thicknesses on the edge of the sheet exists regardless of the type of reactant. As an example, a method and apparatus for a surface reaction that takes place in an oxidation chamber fed with an oxidant is shown below.

  The annealing furnace further includes an oxidation chamber provided with means for adjusting the oxygen concentration of the atmosphere in the region near the edge of the sheet. The oxidation chamber according to the invention can be used in continuous galvanizing lines and continuous annealing lines without hot dip galvanizing equipment. In this latter case, the uncoated steel sheet can be further pickled to remove the oxide layer formed during annealing.

  The method according to the invention consists in injecting an inert gas at a defined flow rate and temperature through the side of the oxidation chamber. For this purpose, as shown in FIG. 2, the oxidation chamber 2 comprises a side for injecting an inert gas in addition to a lateral opening 4 for injecting an oxidant medium (also called oxidant). A side opening 3 is included. In this way, the level of laterally injected oxidant can be increased or decreased in the edge region depending on the dilution rate resulting from the lateral injection of inert gas. Furthermore, as detailed below, the oxidation chamber may further include an opening for extracting fluid to the opposite side of the lateral opening to avoid overpressure inside the chamber.

  According to one embodiment of the present invention, the side opening of the chamber can be in the form of a hole, and one, two or more holes can be provided on each side of the chamber. According to other embodiments, the openings can be in the form of slots or any form suitable for injecting gas.

  In addition, the oxidation chamber can be provided with means for separately controlling the flow rate of the inert gas on each side.

  The lateral opening for injecting oxidant gas through the chamber is preferably located at the top of the chamber for reasons explained below. Openings are located on each side of the sheet. According to one embodiment of the invention shown in FIG. 3, the lateral openings 4 are in the form of slots, but they can have other shapes according to other embodiments. Furthermore, the openings 4 can be provided with reinforcements 6 so as to keep the geometry of the openings constant as represented in FIG.

  On the opposite side of the lateral opening, i.e. at the bottom of the oxidation chamber, if oxidant injection is performed at the top, the chamber is extracted to reduce the pressure inside the chamber when no fluid is circulated. including. They can be in the form of slots on each side of the sheet as shown in FIG. 5, or can be rounded, square or rectangular openings as represented in FIG. .

  The chamber further includes rollers or similar sealing systems at its inlet and outlet to separate the chamber atmosphere from the rest of the annealing furnace and to minimize oxidant flow in other parts of the furnace. For simplicity, only half of the roller 8 closest to the chamber is represented in FIGS. In addition, the chamber is insulated, but some heating devices can be added to compensate for heat loss if necessary.

  As an example, typical dimensions of the oxidation chamber are as follows. It is 3 to 5 meters long and has a width about 150 mm wider than the maximum strip width to travel. A typical design is 2 meters wide for a maximum strip width of 1850 mm. The minimum distance between the oxidation chamber casing and the strip is 75-220 mm, preferably 100-200 mm, more preferably 100 mm.

As shown in FIG. 2, the steel sheet 5 passes through the oxidation chamber 2 in the vertical direction. Sheets can be transported up or down depending on the overall furnace layout. An oxidant gas composed of a mixture of N ₂ and O ₂ having an oxygen content of 0.01 to 8% by volume, preferably 0.1 to 4% by volume, is injected through the lateral opening 4. The oxidant flow rate, temperature, and concentration are controlled. The flow rate per side is typically 150-250 Nm ³ / h for a slot with a 10 mm opening and a 2 m length. The temperature of the mixture N ₂ + O ₂ is 200 ° C. to 50 ° C. below the strip temperature in order to benefit from the buoyancy principle. Preferably, the mixture temperature is 580-600 ° C for a 700 ° C strip. Gas cooler than the strip travels down and for this reason the lateral opening is located at the top of the chamber. Since oxygen is not consumed in the areas adjacent to the sides of the chamber that are outside the strip edge, the concentration of O ₂ is high in those parts, and a thick oxide layer at the edge of the sheet compared to the central part of the sheet Produce. This is especially true for narrow width sheets. To solve this problem, a small amount of pure inert gas such as N ₂ or Ar is injected downstream of the oxidant injection through the side opening of the chamber. The flow rate and temperature of the inert gas is controlled and adjusted depending on the strip grade, strip width, oxygen content, and main oxidant flow rate. The total flow rate is typically 5 to 70 Nm < ³ > / h, preferably 10 to 60 Nm < ³ > / h per side fed through one or more openings. The fluid temperature is 200 ° C. to 50 ° C. below the strip temperature to take advantage of the buoyancy principle. Preferably, the target is 580-600 ° C for a 700 ° C strip. Thereby, the inert gas stream moves downward.

  The following simulation shows the effect of the method and apparatus according to the invention for evenly distributing the oxide layer through the width of the sheet.

1050 mm of a specific composition at 700 ° C. containing 1% O ₂ and running at 120 mpm in an oxidation chamber 3 meters long and 2 meters wide with an oxidant flow of 160 Nm ³ / h per side at 600 ° C. A typical FeO formation on a wide strip is represented in FIG. At the edge of the sheet, the mass per unit surface area of the oxide layer increases by about 30% or more.

Under similar conditions but with 600 ° C. inert gas injected at 40 Nm ³ / h on each side of the chamber, the oxide uniformity is improved as shown in FIG. In this case, the increase between the value at the center of the strip and the maximum value at the edge of the strip is less than 10%. According to the invention, the goal is an increase of less than 15% between the value at the center of the strip and the maximum value at the edge, preferably an increase of less than 10%.

  As already mentioned, for the corrected effect, the correct flow rates and temperatures of the main oxidant and inert gas need to be adjusted with the processed strip width and quality.

  Each flow rate is controlled by a control valve and a flow meter. There is a temperature sensor and the temperature is achieved by a heat exchanger using gas, electricity, etc. All injected gases (oxidant and inert gas) can be circulated or not circulated. The pressure in the chamber is controlled by fluid extraction in the sealing device, but can also be controlled by the extraction slot when no fluid is circulated. This makes it possible to avoid overpressure in the chamber as well as oxidant flow in other parts of the furnace. The extraction flow is regulated by controlling the pressure in the chamber versus the other parts of the furnace. A typical flow control can be done according to the PID principle represented in FIG. The oxide thickness is measured across the strip width by a dedicated system, which is finally installed on each side of the strip after the oxidation zone, which means outside the chamber.

  The present invention has been shown and described for an oxidation chamber having a lateral opening located at the top of the chamber and in which the oxidant and inert gas move downward. Because their temperature is lower than the temperature of the strip. The present description also includes a configuration having a lateral opening located at the bottom of the oxidation chamber. In this case, the extraction zone must be located at the top of the chamber and the inert gas and the main oxidant must be heated above the temperature of the strip in order to move up. The side openings are likewise arranged downstream of the oxidant stream.

  While the invention has been shown and described in detail in the drawings and foregoing description, such illustration and description are illustrative or exemplary and not restrictive. It will be appreciated that variations and modifications can be effected by a person skilled in the art within the scope of the following claims. In particular, the invention encompasses further embodiments having any combination of features from the different embodiments described above and below.

  The terms used in the claims should be considered to have the broadest reasonable interpretation consistent with the preceding description. For example, the use of the article “a” or “the” in introducing an element should not be construed as excluding more than one element. Similarly, a reference to “or” excludes “A and B” unless it is clear from the content or the above description that only one of A and B is intended. Should be interpreted as not.

1 Annealing furnace 2 Reaction zone (also called reaction chamber, especially oxidation zone or oxidation chamber)
3 Side openings for injecting inert gas (also called inert gas openings)
4 Lateral opening for injecting reactants, especially oxidant (also called reactant opening)
5 Strip or sheet 6 Reinforcing material in lateral opening 7 Extraction opening 8 Sealing roller 9 Zinc bath 10 Heating means 11 Valve

Claims (15)

  A continuous annealing furnace (1) for annealing a steel strip (5), the continuous annealing furnace (1) comprising a reaction chamber (2) in which the steel strip (5) is transported vertically, The reaction chamber (2) includes an opening (4) (also referred to as a reactant opening) fed with a reactant, located at the top or bottom of the reaction chamber (2), wherein the reaction chamber (2) is Further comprising another opening (3) (also referred to as an inert gas opening) to which an inert gas is supplied, said inert gas opening (3) being located laterally of the reaction chamber (2), Continuous annealing furnace.   The continuous annealing furnace according to claim 1, wherein the inert gas opening (3) is positioned in such a way that it is downstream of the reactant stream from the reactant opening (4).   The continuous annealing furnace according to claim 1 or 2, comprising one or more inert gas openings (3) on each side of the reaction chamber (2).   The continuous annealing furnace according to any one of claims 1 to 3, comprising means for controlling the flow rate and temperature of the inert gas.   The continuous annealing furnace according to any of claims 1 to 4, further comprising means for separately controlling the flow rate of the inert gas on each side of the reaction chamber (2).   The reaction chamber (2) includes an extraction opening (7) for avoiding overpressure inside the reaction chamber (2), said extraction opening (7) comprising a reactant opening (4) and an inert gas opening ( 6. A continuous annealing furnace according to any one of the preceding claims, positioned so as to be downstream of the reactant stream and inert gas stream leaving 3) respectively.   The distance between the side of the reaction chamber (2) and the edge of the steel strip (5) is 75-220 mm, preferably 100-200 mm, more preferably 100 mm. Continuous annealing furnace.   A continuous annealing furnace according to any of the preceding claims, wherein the reaction chamber (2) comprises a reactant opening (4) facing each side of the steel strip (5).   The continuous annealing furnace according to any one of claims 1 to 8, wherein the reaction chamber (2) is an oxidation chamber and the reactant is an oxidant.   The method according to any one of claims 1 to 9, comprising the step of injecting an inert gas from the side in the reaction chamber (2) and the step of injecting a reactant upstream of the inert gas flow in the reaction chamber (2). Method for controlling surface reactions on a steel strip (5) running vertically through a reaction chamber (2) of a continuous annealing furnace (1) as described.   11. The reaction chamber (2) is an oxidation chamber, the reactant is an oxidant, and the oxygen content of the oxidant is 0.01 to 8% by volume, preferably 0.1 to 4% by volume. The method described. The method according to claim 10 or 11, wherein the flow rate of the inert gas is 5 to 70 Nm ³ / h, preferably 10 to 60 Nm ³ / h.   When the reaction of the steel strip (5) is carried out by injecting the reactants into the top of the reaction chamber (2), the inert gas temperature is 200-50 ° C. below the steel strip temperature, and the reaction of the steel strip (5) The process according to any of claims 10 to 12, wherein when the is carried out by injecting the reactants into the bottom of the reaction chamber (2), the inert gas temperature is 200-50 ° C higher than the steel strip temperature.   There is a step of extracting a gas containing an inert gas and a reactant, the flow rate of the extracted gas being based on the pressure difference between the inside of the reaction chamber (2) and the other part of the continuous annealing furnace (1). The method according to claim 10, wherein the method is calculated as follows.   The steel strip (5) has an oxide layer at the outlet of the oxidation chamber (2), the mass of the oxide layer per surface area between the value at the center of the steel strip and the maximum value at the edge of the steel strip. Steel strip (5) obtained by the method according to any of claims 11 to 14, wherein the increase is less than 15%, preferably less than 10%.